1. Field of the Invention
The present invention relates to novel compositions of matter based on a polyamide which has been fireproofed by means of a red phosphorus material, and which are particularly adopted for the production of shaped articles for the electrical and electronics industries. This invention especially relates to novel polyamide-based molding compositions adopted for the production of fireproofed shaped articles providing a good compromise of properties, in particular in respect of flame resistance, resilience, arc tracking resistance, and surface appearance.
2. Description of the Prior Art
It is known to this art that the addition of red phosphorus to polyamide-based compositions permits a high degree of fireproofing to be imparted thereto.
U.S. Pat. No. 3,883,475 describes fireproofed polyamide-based compositions in which attempts have been made to inhibit the release of very highly toxic phosphine, which forms as a result of a disproportionation reaction of red phosphorus under the influence of trace amounts of water which are present in the polymer and of the high temperature required for its conversion, by adding to the composition a metal compound, advantageously cupric oxide.
An improvement has been proposed in French Patent No. 2,367,100, namely, the use of cadmium oxide instead of CuO. In addition to its effectiveness (which is at least equal to that of CuO) in inhibiting the release of phosphine, cadmium oxide also enables production of shaped articles exhibiting a particularly high arc tracking resistance (within the meaning of NF Standard C 26,220), which is equal to or higher than 400 volts in the case of unfilled compositions and 375 volts in the case of compositions filled with more than 25% by weight of glass fibers.
In French Patent No. 2,553,783, a material to replace cadmium oxide (which exhibits some degree of toxicity) has been proposed, comprising of a lanthanide-based compound. With this adjuvant, the resulting fireproofed polyamide-based compositions can be shaped into articles offering a better compromise of properties, in particular in respect of fireproofing, resilience and arc tracking resistance, as opposed to the advantages associated with the use of cadmium oxide. Compare also U.S. Pat. No. 4,559,372.
However, serious problems remain concerning the appearance and the development, to a variable degree, of whitish stains (whitish bloom) on the surface of the articles fireproofed by means of red phosphorus, when these articles are subjected to the twin effect of a high temperature and of moisture. Problems of this type are encountered, for example, in hot, humid tropical countries.
Cf. U.S. Pat. No. 4,092,284.